ecology of phasmids - KLUEDO - Universität Kaiserslautern

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Community structure & host range 14 where H’MAX = Maximum possible value of the Shannon-Wiener Function S = Number of species in the community Eveness ranges from 0 to 1. Generally all eveness measures are overestimated (see Krebs 1989) as they assume that the total number of species in the community is known. However, in the presented study this problem may be of minor importance as the phasmid community in forest understory and at forest edges was sampled excessively. On the base of line-transect data I calculated population density of the phasmid community and in particular population density of M. diocles for forest understory and forest edges separately. Generally population densities from line-transect data can be calculated as described by Krebs (1989): Equation 2-4 n D = 2La where D = Density of animals per unit area n = Number of animals seen on transect L = Length of transect a = Constant that describes the probability of detecting an animal The estimation of the detection probability a affords knowledge of sighting distance and angle for each animal measured from the transect line. These parameters could not be assessed because for detection of nymphs the undersides of leaves had to be searched and therefore I had to leave the central transect lines. Consequently, I simplified the calculation of density by assuming that detection probability was 1 (i.e., all animals were found) and thereby that ‘a’ was negligible (density estimates based on numbers of observed animals solely are sometimes referred to as apparent density; Krebs 1989). This assumption may have lead to an underestimation of densities, as it was likely that animals were missed. Further, I accounted for the fact that in the understory line-transects were searched on both sides while at forest edges they were sampled one-sided facing the forest (width of 2 m). Accordingly, in transects of 80 m length, the corresponding searching area in the understory was 320 m 2 versus 160 m 2 at forest edges. These modifications led to the calculation of population densities by: n n D = for forest understory, and D = for forest edges, 2Lw 1Lw where w is the one-sided monitored width of the transect. Resulting phasmid densities (ind.*m -2 ) for transects were averaged on habitat level per monitor date (28 monitoring dates and three transects per habitat). To allow for comparison I extrapolated densities to the base of number of individuals per hectare searching area (ind.*ha -1 ). Under the assumption that phasmids would show a pronounced seasonal pattern in densities, I expected higher densities of phasmids (and particularly of nymphs) in the early rainy season. Seasonal variation in abundances for nymphs and adults was compared on the base of cumulative absolute abundances on a monthly scale. As data for the forest understory were few, I only analyzed abundances in forest edges. Data for November 2000 and July 2001 were excluded from the analysis, because only one monitor date
Community structure & host range 15 was available for each of these months. I tested for temporal heterogeneity of absolute abundances by comparing observed and expected abundances in Chi-Square Goodness-of-Fit Tests (GOF). Although data for phasmid abundances may not be independent, e.g. because of contagiousness, GOF analysis is appropriate if the user is only interested in heterogeneity or homogeneity (Fowler et al. 1998). 2.2.3.2 Estimating niche dimensions and overlap As one dimension of niche breadth, I assessed diet breadth using the potential food resources (i.e. plant families) registered along line-transects. Because none of the four tested phasmid species was specialized below the family level, all niche measures were expressed on the plant family level, i.e. each potential host plant family represented a resource state. As measure for uniformity of distribution of individuals among the resource states I used Levin’s standardized measure of niche breadth BA: Equation 2-5 B A B −1 = n −1 where BA = Levin’s standardized niche breadth B = Levin’s measure of niche breadth state j n = Number of possible resource states 1 B with pj = Proportion of individuals found in resource = 2 p j ∑ Levin’s standardized measure of niche breadth ranges from 0 to 1. BA is maximal when a species does not discriminate among resource states. Overlap in the use of food niches among phasmid species was calculated by Pianka’s measure of niche overlap Ojk: Equation 2-6 O jk = n ∑ pij p 2 ∑ pij∑ where Ojk = Pianka’s measure of niche overlap between species j and species k pij = Proportion resource i is of the total resources used by species j pik = Proportion resource i is of the total resources used by species k Pianka’s measure of niche overlap ranges from 0 (complete separation of niches) to 1 (complete overlap). To describe overlap between realized food niche (i.e. potential host plant families from line-transects) and absolute food niche (i.e. plant families accepted in feeding-trials) I used Sørensen’s coefficient of similarity SS: Equation 2-7 SS 2a = 2a + b + c where SS = Sørensen’s similarity coefficient a = Number of plant families recorded in line-transect and accepted in feeding-trials b = Number of plant families only recorded in line-transect records but not accepted in feeding-trials ik p 2 ik
Page 1 and 2: ECOLOGY OF PHASMIDS (PHASMATODEA) I
Page 5 and 6: ECOLOGY OF PHASMIDS (PHASMATODEA) I
Page 7 and 8: Acknowledgements I Acknowledgements
Page 9 and 10: Table of Contents III 3 Life cycle,
Page 11 and 12: List of Figures V List of Figures F
Page 13: List of Abbreviations VII List of A
Page 16 and 17: Introduction 2 Regardless whether s
Page 18 and 19: Introduction 4 Description of phasm
Page 20 and 21: Introduction 6 Solanum and Piper (T
Page 22 and 23: Introduction 8 1.3.4 Data analysis
Page 24 and 25: Community structure & host range 10
Page 46 and 47: Life history & potential population
Page 58 and 59: Adult female feeding preference & n
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Adult female feeding preference & n
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Predation mediated mortality & migr
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Concluding remarks 91 6 Concluding
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Abstract 93 7 Abstract Herbivory is
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Literature cited 96 Basset, Y. 1997
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Literature cited 98 Brown, B. J., M
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Literature cited 100 Croat, T. B. 1
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Literature cited 102 Hagerman, A. E
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Literature cited 104 Kearsley, M. J
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Literature cited 106 McNeill, S., T
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Literature cited 108 Reich, P. B.,
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Literature cited 110 Strong, D. R.,
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Appendix 113 9 Appendix Please cont
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Appendix 1: Phasmid species previou
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Tabellarischer Lebenslauf Angaben z
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Berger J., Schaefer, M., 1997. Wild
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